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OSLO (Reuters) - Quickening climate change in the Arctic including a thaw of Greenland's ice could raise world sea levels by up to 1.6 meters by 2100, an international report showed on Tuesday.

Such a rise -- above most past scientific estimates -- would add to threats to coasts from Bangladesh to Florida, low-lying Pacific islands and cities from London to Shanghai. It would also, for instance, raise costs of building tsunami barriers in Japan.

"The past six years (until 2010) have been the warmest period ever recorded in the Arctic," according to the Oslo-based Arctic Monitoring and Assessment Programme (AMAP), which is backed by the eight-nation Arctic Council.

"In the future, global sea level is projected to rise by 0.9 meters (2ft 11in) to 1.6 meters (5ft 3in) by 2100 and the loss of ice from Arctic glaciers, ice caps and the Greenland ice sheet will make a substantial contribution," it said. The rises were projected from 1990 levels.

"Arctic glaciers, ice caps and the Greenland ice sheet contributed over 40 percent of the global sea level rise of around 3 mm per year observed between 2003 and 2008," it said.

Foreign ministers from Arctic Council nations -- the United States, Russia, Canada, Sweden, Finland, Denmark, Norway and Iceland -- are due to meet in Greenland on May 12. Warming in the Arctic is happening at about twice the world average.

WORRYING

The United Nations' Intergovernmental Panel on Climate Change (IPCC) said in its last major report in 2007 that world sea levels were likely to rise by between 18 and 59 cm by 2100. Those numbers did not include a possible acceleration of a thaw in polar regions.

"It is worrying that the most recent science points to much higher sea level rise than we have been expecting until now," European Climate Commissioner Connie Hedegaard told Reuters.

"The study is yet another reminder of how pressing it has become to tackle climate change, although this urgency is not always evident neither in the public debate nor from the pace in the international negotiations," she said.

U.N. talks on a global pact to combat climate change are making sluggish progress. The United Nations says national promises to limit greenhouse gas emissions, mainly from burning fossil fuels, are insufficient to avoid dangerous changes.

The AMAP study, drawing on work by hundreds of experts, said there were signs that warming was accelerating. It said the Arctic Ocean could be nearly ice free in summers within 30 to 40 years, earlier than projected by the IPCC.

As reflective ice and snow shrink, they expose ever bigger areas of darker water or soil. Those dark regions soak up ever more heat from the sun, in turn stoking a melt of the remaining ice and snow.

"There is evidence that two components of the Arctic cryosphere -- snow and sea ice -- are interacting with the climate system to accelerate warming," it said.

The AMAP report was due for release on Wednesday but AMAP officials released it a day early after advance media leaks.